1. Field of the Invention
The present invention relates to a cut sheet feeder for use with the image forming apparatus such as a copier or a printer, the feeder feeding the apparatus with cut sheets of recording paper.
2. Description of the Related Art
The image forming apparatus is most often used to record images on a large number of cut sheets of the same size which are fed continuously (e.g., from a sheet feed table for bulk printing). But occasionally, it is desired to interrupt the ongoing process of image printing involving many cut sheets so as to insert image printing of a different kind typically on a smaller number of sheets (fed typically from a cassette). Some of the conventional cut sheet feeders for use with the image forming apparatus have mechanisms that meet the requirements for the on-demand inserted printing.
FIGS. 8(a) and 8(b) are perspective views showing a conventional image forming apparatus equipped with a cut sheet feeder capable of feeding sheets either from a sheet feed table or from a cassette. In the figures, the cut sheet feeder 91 is attached to one side of the image forming apparatus 90. The cut sheet feeder 91 comprises a frame 92 mounted retractably from the feeder body 91a, pick-up rollers 93 attached to a top side of the frame 92, a sheet feed table 95 which moves up and down inside the frame 92 and which has a large number of cut sheets 94 stacked thereon, and a sheet guide 96 adjustable in the longitudinal direction of the cut sheets 94 on the sheet feed table 95. Distinct from the cut sheet feeder 91, cassettes 97 are mounted removably in the image forming apparatus 90. They have different sizes that correspond to the sizes of cut sheets.
The above type of conventional cut sheet feeder has a plurality of sheet feed mechanisms positioned near the sheet feed table 95 and the cassettes 97, each mechanism comprising its dedicated pick-up rollers (only the rollers for the sheet feed table are shown), guide plates and other related parts. When an operator selects a desired sheet type, the corresponding sheet feed mechanism is activated. The activated mechanism picks up cut sheets one by one from the sheet feed table 95 or from the corresponding sheet cassette 97 and feeds them into a predetermined position inside the image forming apparatus 90.
The conventional cut sheet feeder of the above-mentioned type has as many sheet feed mechanisms as the number of the sheet feed table 95 and the sheet cassettes 97 that are mounted in advance of feed operation. The cut sheet feeder also has a plurality of sheet transport routes for guiding cut sheets from the multiple storage locations via rollers to a common feed position. These features make the cut sheet feeder bulky, complex, and thus prone to feed-related troubles.